To overcome the limitations of RBAC and CapBAC models in terms of nature of access rights (i.e., static), assignment level (i.e., coarse-grained), reduce the computation cost of generating tokens and provide dynamic authorisation of IoT devices, ABAC models are frequently deployed. In ABAC models, different attributes are used to grant access privileges to IoT devices. By utilising the device attributes of the ABAC models in IoT-based networks to provide secure access to underlying resources, Yutaka et al. [1]} proposed a Blockchain-based access control scheme by utilising the smart contracts to write and enforce the policies. In this scheme, a range of smart contracts, from registration of attributes to defining the ABAC policies, is written and executed on Ethereum Blockchain. Finally, the proposed scheme is deployed on the Local Ethereum Blockchain to demonstrate its feasibility and evaluate its monetary cost. An extension of the previous work [1]} is presented in the [3]}, with a focus on enhancing performance evaluation parameters such as deployment and operating cost. Wang et al. [4]} proposed a Blockchain-based distributed access control framework for IoT networks by utilising the subject and objects based attributes. In this framework, attributes such as manufacturer and object specifications provide a finer-grained degree of access control for resource-constrained IoT devices. Liu et al. [5]} introduced Fabric-IoT, a fabric-based access control system that leverages the ABAC and Hyperledger fabric Blockchain architectures to enable dynamic and fine-grained access control rights for IoT networks. Three smart contracts with distinct functionality (device, policy, and access) are created and deployed on the Blockchain in this scheme to ensure the secure execution of access rights. For access rights and delegation of access rights in IoT based networks, Ali et al. [6]} proposed a decentralised Blockchain-based architecture called xDBAuth, in which the smart contracts are written and deployed hierarchically, providing permission assignment and access control for both local and global devices, as well as authenticating in their parent IoT domains. A similar approach to [5]} is given in [8]}, with the goal of providing data sharing and access control across IoT devices via the use of Blockchain and smart contracts. Qin et al. [9]} utilised an ABAC model to propose a lightweight blockchain-based access control scheme called LBAC. Blockchain is used instead of untrusted cloud servers to perform the outsourcing decryption on attributes determining the secure access to resources. To achieve the dynamic nature of authorisation mechanisms for IoT networks, Putra et al. [10]} presented a decentralised access control mechanism based on the ABAC model in conjunction with a trust and reputation system. The proposed mechanism sought to achieve dynamic access privileges by focusing on IoT device compromise scenarios.
